1. Field of the Invention
The invention relates to a damper device for a vehicle that is provided between an engine and a drive unit incorporating a motor-generator, and more particularly to a technique for setting an optimum hysteresis torque.
2. Description of Related Art
A configuration is available in which a hysteresis mechanism generating a hysteresis torque is provided in a damper device for a vehicle that is installed between an engine and a drive unit incorporating a motor-generator and transmits power while absorbing torque fluctuations generated by the engine. For example, such a damper device is described in Japanese Patent Application Publication No. 2006-29363 (JP 2006-29363 A). In the damper device described in JP 2006-29363 A, a technique is used by which when a relative torsion angle in the torsion in the positive direction in which the torque is transmitted from the engine side is equal to or less than a predetermined value, a small hysteresis torque is generated, whereas when the relative torsion angle exceeds the predetermined value, a large hysteresis torque is generated, and in the case of torsion in the negative direction in which the torque is transmitted from the drive unit side, a large hysteresis torque is generated.
However, for example, during idle operation of the engine, since small torsional vibrations are generated, it is desirable that the vibrations be attenuated by a small hysteresis torque. For this purpose, in the damper device described in JP 2006-29363 A, vibrations occurring during idle operation and the booming sound occurring during normal engine operation are attenuated by generating a small hysteresis torque when the relative torsion angle is equal to or less than a predetermined value in the torsion in the positive direction in which the torque is transmitted from the engine side. However, in the damper device described in JP 2006-29363 A, since switching between a small hysteresis torque and a large hysteresis torque is performed on the basis of the relative torsion angle, a large hysteresis torque can be generated when a small hysteresis torque, such as that during idle operation or normal engine operation, is desired, and the driver can feel uncomfortable.